My KDE4 mem when booting to KDE 4.7.3 is 4xx MB. I'm afraid it'll not enough if it just 512MB mem (unless you kill akonadi & nepomuk). Barely usable. It'll run slowly cause then have to use swap space.

When you just have 512MB mem, when booting to KDE, Try to you open firefox with 4-6 tab, a couple of program and you'll run out of mem.

I really like KDE, but their mem footprint is worse with each release. Memory's cheaper now doesn't meant KDE have to throw all the memory they can use.

Having said that, really, buying a bit more memory is really the easiest and most effective way to to go. "

I ran KDE4 versions prior to 4.4 on a 450mhz P2 with 384MB ram After my P4 system died. It an as fast as KDE 3.5.x and alot snappier over time than the XP partition. And it ran very well on an old P3 700mhz 256MB laptop that I played with.

Worked fine for me on a 2.8 GHz Celeron laptop with only 512 MB of RAM, running KDE4 plasma-netbook interface. Could run Firefox and even watch youtube videos (until a certain Flash upgrade hosed the box and the reinstall never ran Flash properly afterward).

Yes, desktop effects are turned off (the onboard RADEON 7000 GPU doesn't support them), nepomuck/akonadi are turned off (it's an HTPC, no need for strigi or mail storage), and it tends to only run 1 app at a time (Dragon). But KDE4 runs beautifully on it, and it's very usable. It was our main TV show/movie access for several years, starting with KDE3, then upgrading to KDE4.2, then 4.4, and I think it was running 4.6 by the end.